PCI-E x8 and x16 issues

without knowing anything about that specific motherboard, most graphics cards should work with fewer PCI-E lanes. When PCI-E first came out Toms did an article testing 8x, 4x, and 1x by blocking parts of the connector off and at least on... I think it was an X850... it ran fine all the way down to 4x without much of a performance hit. In fact they had more trouble with low-end cards that don't have secondary power connectors because the limited PCI-E bus delivered less power.

-mcg

i have ecs gefrce6100sm-m motherboard and i have a geforce 7600Gt installed in the pci-e x16 slot and it works fine in x8 mode.

Power and Bandwidth are TWO very different issues, a PCI-E x16 slot is able to supply up to 75W regardless of it being set in x8 or x16 I believe, if you're card isn't getting enough power is because it requires an external connection (if your card doesn't have an external plug, then it doesn't require more power than what the slot can provide).

However Bandwidth is a completely different thing, it's basically how much data can travel through the slot, most cards do not have bandwidth issues set on either x8 or x16 (the 8800GTS/GTX might be different, I can't remember but I don't think so), so unless you are considering to get a 8800GTX, you shouldn't worry about the PCIe slot set at x8.

EDIT: The X1950 and 7900/7950 card series all require external power to function properly.

Yes, but before you go buying something, what PSU do you have? Just because your PSU has a cable doesn't mean it can supply enough power to the card.

Antec is a very good PSU maker, however it depends on WHICH antec model you have, because they make something for every customer (Silent PC, Low end, Mainstream, enthusiasts, and extreme users).

I also have ECS mobo and it alsa says PCI-E x8 so i think its time to change mobo to some other brand.